POLYMERS
Polymers (poly-many; mers-parts) are macromolecules (large molecules) of high molecular
masses built up by joining together of a large number of small molecules (called monomers).
For example, ployethane is formed by linking together of a large number of ethane (C2H4)
molecules.
Thus, small molecules which combine with each other to form polymer molecules, are called
monomers.
CLASSIFICATION OF POLYMERS
Polymers can be classified by number of ways:
1) Classification on the basis of source:
(i) Natural polymers- These are found in nature in animals and plants. For example, starch,
cellulose, proteins etc.
(ii) Synthetic polymers- These are man-made polymers. For example, Polyethylene,
Polypropylene, Polystyrene, Nylon, Polyvinylchloride (PVC) etc.
2) Classification on the basis of structure:
(i) Linear polymers are those polymers in which monomers are joined in the form of long
straight chains. For example, Nylons, Polyethene etc.
(ii) Branched polymers are linear but also have some branches with main chain. For example,
glycogen etc.
(iii) Cross linked polymers are those polymers in which monomers are joined each other by
covalent bonds. For example, Bakelite etc.
3) Classification based on molecular forces:
(i) Thermoplastic polymers are linear, long chain polymers which can be softened on heating
and hardened on cooling reversibly. Thus they can be formed again and again. For example,
polyethene, polypropylene, nylons, teflon etc.
(ii) Thermosetting polymers are those polymers, which during heating get hardened and they
can not be softened. These polymers have crosslinked structure. For example, Bakelite,
polyester etc.
(iii) Elastomer (or synthetic rubber) is rubber like polymer, which can be stretched to at least
thrice its length, but returns to its original shape as soon as stretching released.
MECHANISM OF POLYMERIZATION
Polymerization reaction generally involves three steps: Initiation, Propagation and
Termination. For example,
Cationic mechanism of polymerization involves the following steps:
(i) Initiation:
(ii) Propagation:
(iii) Termination:
COAL
Coal is formed from the fossilized remains of animals and plants, hence it is also known as
fossil fuel.
The advantages of using coal are its availability, low cost, least risk of fire hazards and easy
to storage.
ANALYSIS OF COAL
In order to analyse the quality of coal, there are two types of analysis:
Proximate analysis- It involves the following determinations:
(i) Moisture content- High percentage of moisture is undesirable because it increases the cost
of the coal. Hence the lower the moisture content, better the quality of coal as a fuel.
Determination of moisture: It is the loss of weight of coal when heated at about 1050C in a
crucible. A known amount of the finely powdered coal sample, taken in a silica crucible, is
heated in an oven at 105-1100C for about 1 hour. After that crucible is taken out, cooled and
weighed.
% of moisture =
Loss in weight
× 100
Weight of coal taken
(ii) Volatile matter- The volatile matter present in the coal may be combustible gases (such as
hydrogen, methane, CO etc) and non-combustible gases (such as CO2 and N2).
A high volatile matter containing coal burns with long flame and high smoke. Hence , lesser
the volatile matter, better the quality of coal.
Determination of volatile matter: The moisture free coal is taken in silica crucible and
covered with lid. It is then placed in an furnace at 9250C for 7 minutes. The crucible is then
taken out and cooled.
% of volatile matter = Loss of weight due to removal of volatile matter
Weight of coal taken
× 100
(iii) Ash- Ash is non-combustible useless matter which is left behind when coal have been
burnt off. It is undesirable because it reduces the calorific value of coal and burning of coal
becomes irregular. Hence, lower the ash, better the quality of coal.
Determination of ash: It is obtained after burning a weighed amount of dry coal in an open
crucible (i.e., in presence of oxygen or air) at 700-7500 C for half an hour in furnace.
% of ash =
weight of ash
× 100
Weight of coal taken
(iv) Fixed Carbon- After the determination of moisture, volatile matter and ash, the remaining
is known as fixed carbon. Higher the % of fixed carbon, greater the calorific value and better
is the coal.
% of fixed carbon C = 100 – % of (moisture + volatile matter + ash).
Example. 1.5 gm of coal was weighed into a silica crucible. After heating for one hour at
1000C, the residue weighed 1.415 gm. The crucible was then covered and strongly heated for
exactly seven minutes at 9500 C. The residue weighed 0.528. The crucible was then heated
without the cover, until a constant weight was obtained. The last residue was found to weight
0.254 gm. Calculate the percentage results of the above analysis.
Ans. (a) Moisture (%) = Loss in weight
× 100
Weight of coal taken
= 1.5-1.415
× 100
= 5.67%.
1.5
(b) % of volatile matter = Loss of weight due to removal of volatile matter
Weight of coal taken
1.415- 0.528
× 100
= 59%
1.5
(c) Ash (%) = weight of ash left
Weight of coal taken
0.254
1.5
× 100
=
16.93%.
× 100
× 100
(d) Fixed Carbon (%) = 100 - % of (moisture+ volatile matter + ash)
= 100 – (5.67+59+16.93) = 18.4 %.
GLASS
Glass is a super-cooled liquid consisting of a mixture of silicates. The basic building block of
ordinary glass is tetrahedron built from a silicon atom at the centre and four oxygen atoms
directed along the four corners of tetrahedron. The tetrahedron join together to give a threedimensional interlocking structure that gives glass its high viscosity. When heated, glass does
not melt sharply but it gradually softens until it becomes liquid. Thus, glass can be moulded
into any desired shape. It is this property of glass which makes it a highly useful material
since a number of objects of different shapes and forms can be made out of it.
Glass is a solid solution which may be represented as
x R2O. y MO. 6 SiO2
where x and y are whole numbers, R is an atom like Na, K etc., M is an atom like Pb, Ca, Zn
etc.
Manufacture of glass
Raw materials:
(a) Sodium is soda ash (Na2CO3)
(b) Potassium is potash (K2CO3)
(c) Calcium are limestone (CaCO3) or chalk or lime Ca(OH)2
(d) Lead PbO
(e) Silica are white sand, quartz.
(f) Zinc is zinc oxide (ZnO)
(g) Phosphorous is P2O5
(h) Borate are boric acid and borax
Some other raw materials are incorporated(i) Colouring agents- Important colouring agents are: Cr2O3 (yellow-green), CoO (blue), CuO
(red), Fe2O3 (brown), Na3AlF6 (milky white), MnO2 (purple) etc.
(j) Cullet- Cullet is a crushed glass of defective or broken glass particles.
Manufacturing steps
The manufacture of glass can be divided into four steps:
(i) Melting (ii) Shaping and forming (iii) Annealing (iv) Finishing
Step 1. Melting: Raw materials mixed with cullets and finely divided to get an mixture (called
batch). Melting of glass batches is carried out either in pot furnace or in tank furnace.
Colouring and decolouring agents are added at this stage. Heating is continued and then glass
is cooled to about 8000C.
Step 2. Shaping and Forming: Desired shaped articles are made from molten glass by
pressing between rollers.
Step 3. Annealing: Annealing is the very slow cooling of manufactured glass articles, in order
to reduce strain. The quality of glass is better if it is annealed for longer period.
Step 4. Finishing: After annealing, all glass articles are subjected to finishing process such as
cleaning, polishing, cutting etc.
Types of Glasses
(i) Soda-lime glass or soft glass
It is the simplest silicate glass in which Na2O is added for melting the silica glass. It is made
by fusing the sodium carbonate, calcium carbonate and SiO2. Its approximate composition is
Na2O. CaO. 6SiO2
Properties: Low cost, resistant to water
Applications: Soda lime glass is widely used for(a) Window glasses
glassware.
(b) Cheaper tablewares like bottles, jars etc.
(ii) Potash glass or Hard glass
Its approximate composition is K2O. CaO. 6 SiO2
Properties: it is harder in comparison to soda glass.
Applications: It is used for chemical apparatus.
(c) Cheap laboratory
(iii) Lead glass
Its approximate composition is K2O. PbO. 6 SiO2
Properties: Lead glass is bright and it is much easier to shape it.
Applications: Lead glass is widely used for making high quality tablewares, lenses, prisms
and X-ray in medical field.
(iv) Borosilicate glass
Borosilicate glass contains boron trioxide (B2O3) and is very rich in silica and little amount of
alumina.
The percentage composition of different components would be
Component
SiO2
(%)
80.5
B2O3
13
Al2O3
3
K2O
Na2O
3
0.5
Properties: Borosilicate glass has high chemical resistance, shock proof.
Applications: Borosilicate glass is widely used in superior laboratory apparatus like flasks,
beakers etc., kitchenware, television tubes, pipelines.
(v) Alumino silicate glass
Alumino silicate glass has higher percentage of Al2O3 and lower percentage of B2O3,
compared to borosilicate glass.
The percentage composition of different components would be
Component
(%)
SiO2
B2O3
55
7
Al2O3
23
MgO
CaO
9
5
Na2O+K2O
1
Applications: It is used for certain domestic equipment.
(vi) Optical glass
Optical glasses are used in optical instruments because they possess
(a) Low viscocity (b) Absence of impurity like iron and thus colorless (c) Ability to take on
the desired polish.
Optical glasses contain phosphorus and lead silicate.
(vii) Toughened glass
Properties: Toughened glass is more elastic.
Applications: Toughened glass is used for making window of trucks, cars, aeroplanes and for
automatic opening doors.
(viii) Photochromic glass
Photochromic glasses change color in the presence of high energy radiation (usually ultraviolet radiation) but reverts back to their original appearance in the absence of radiation.
Applications: Photochromic glass is used in the manufacture of lenses of spectacles and
window glass in homes for better climate control.
CEMENTS
Cement is a material which have adhesive and cohesive properties and capable of binding
materials like bricks, stones etc.
Hydraulic cementing materials are capable of setting and hardening under water while non
hydraulic cement harden in air cannot be used in water.
GYPSUM
The mineral gypsum (CaSO4.2H2O) is extensively used as a raw material for the manufacture
of plasters.
PLASTER OF PARIS (CaSO4.1/2 H2O) is produced by heating gypsum to a temperature of
about 120-1600C.
120-160C
CaSO4.2H2O
CaSO4.1/2 H2O
CLASSIFICATION OF CEMENT
1. Natural cement- is made by naturally occurring clay containing limestone at high
temperature. It possesses hydraulic qualities.
2. Puzzolana cement- is the oldest cement. It was invented by Romans. It form hydraulic
cementing materials when mixes with lime without the use of heat.
3. Slag cement
4. Portland cement- is the most important and reliable cement used for construction works.
MANUFACTURE OF PORTLAND CEMENT
Raw materials for the manufacture of cement are:
1. Calcareous materials, CaO,
2. Al2O3 and SiO2,
3. Powdered coal,
4. Gypsum
Manufacturing of Portland cement involves the following steps:
1) Mixing of raw materials
a) Dry process- The raw materials [limestone or chalk and clay] are crushed into 2-3 cm size
pieces. Then these are ground to fine powder in ball mill. Then the powderd materials are
mixed to get dry raw mixture and kept ready to be in rotary kiln.
b) Wet process- The calcareous raw materials are crushed, powdered and store in big tanks
and then mixed with water in wash mills. When they mixed,a paste is formed called slurry.
The slurry is ready to get into rotary kiln.
2) Burning
Burning is usually done in rotary kiln which is a steel tube, about 2.5 to 3.0 m in diameter
and 90 to 120 m in length. The kiln is capable to rotate. A long hot flame is produced, which
heats the interior of the kiln upto a maximum temperature of 17500C.
Process: The raw mix is injected into kiln at its upper end while hot flames is forced into the
kiln from the lower end. Due to rotation of the kiln, the materials is move continuously
towards the hottest end at the speed of about 15 m per hour.
Chemistry: (i) In the upper part of kiln, where the temperature is around 4000C, most of the
water in the slurry gets evaporated.
(ii) In the central part of kiln, where the temperature is around 10000C, dry mix undergoes
decomposition.
(iii) In the lower part of kiln, the temperature is between 1500 to 17500C. Here lime and clay
undergoes chemical reaction.
The aluminates and silicates of calcium then fuse together to form small, hard, greyish stones
called clinkers. These clinkers are very hot (at about 10000C). The clinkers then kept to be
cool and are collected in small trolleys.
3) Grinding
The cooled clinkers are ground to a fine powder in ball mills. During grinding, small amount
of gypsum is added.
4) Packing
The ground cement is stored in bag by automatic packing machine.
CHEMICAL COMPOSITION OF PORTLAND CEMENT